Insect plagues cause a drastic reduction of crops and insecticides are the traditional method to combat them. The use of insecticides has problems such as:
Their toxicity for humans and superior animals, which causes governments to impose more restrictive regulations for the use thereof.
The lack of selectivity, that converts into the destruction of beneficial insects, or of natural predators of the plague that is to be fought
The resistance developed by insects which makes it necessary to increase more and more the dosage to maintain the effectiveness thereof.
All of these problems oblige insecticide manufacturers to dedicate more and more resources to R+D in order to obtain better products, but the problem continues to exist.
Society demands respect for the environment but at the same time it requires quality of the agricultural food products, which requires the development of new plague control systems based on environmental methods.
The communication among insects is basically done by means of emitting chemical substances, (semiochemicals); the knowledge of said semiochemical substances and of the information that they transmit, provide an environmental method in order to control the behavior of the insects. By means of the artificial emission of synthetic semiochemicals, a specific message is transmitted to a specific species of insects, inducing a response; if the message is of attraction, the response of the insect will be directed towards the emitter. Taking advantage of this inducing capacity the behavior of insects, techniques that permit the control thereof have been developed. The most important ones are:
Control, whose purpose is to prevent the occurrence of plagues, to follow their development and to confirm their extinction by means of a count of the captures that are produced in traps provided with an emitter of an attracting semiochemical.
Sexual confusion, that seeks to prevent the reproduction of insects by means of the emission of amounts of a semiochemical that saturates the receptor organs of the insect preventing it to find members of its same species and of the opposite sex.
Massive captures, that seek to significantly reduce the insect population, by means of captures, in traps, with an attracting semiochemical. Aside from the attractant, a toxic agent for the insect, a sexual sterilizer, an entomopathogenic microorganism or simply glue where the insect is adhered and dies, may also be placed in the traps.
The low toxicity of semiochemicals, their high specificity (their action is directed towards a single species), the difficult occurrence of resistances and their non-existent polluting impact, represent outstanding advantages in contrast to conventional insecticides.
So that the use of these semiochemical substances is effective it is necessary to have physical supports capable of emitting the semiochemicals in a controlled manner for a sufficient amount of time, in such a way that a concentration in the air capable of causing the desired response in the insect in a continued manner is achieved.
The emitters must comply with a series of requirements so that their use is effective to:
Provide an adequate emitting speed
Permit prolonged duration of the emission
Avoid degradation of the semiochemicals
Not produce contaminating residues
Be economical and have easy application
Although there is a large variety of emitting supports on the market such as rubber septa (Aldrich Co., UK; The West Co., Pennsylvania; Arthur H. Thomas Co.; Maavit Products, Tel Aviv, Israel), polyethylene pipes (Shin Etsu Chemical Co., Tokyo, Japan), porous plastic laminates (Hercon Lab. Co., New Jersey, USA); capillary fibers (Albany International, Massachusetts, USA), microcapsules (ICI Agrochemicals, Berks, UK), none of these emitting supports comply with all the above mentioned requirements.
Inorganic molecular sieves being used as carriers for semiochemical substances are known from WO-A-9601052, U.S. Pat. No. 4170631 AND WO-A-9639824. Although such carriers are as such inexpensive, the emitters described in these publications are not easily and unexpensively adaptable to different release rates and to the specific needs of different semiochemicals.
The object of this patent is the preparation and use of supports for controlled emission of semiochemicals, based on the modification of the physicochemical properties of zeolites and other inorganic molecular sieves, in such a way that they provide an emission kinetics adapted to the specific properties of each pheromone.
Inorganic molecular sieves (IMS) have a complex network formed by an assembly of micro or meso pores (xe2x88x85 greater than 14 xc3x85) and cavities, providing the assembly with a high specific surface and a high adsorption capacity. The most important IMS are zeolites, chemically they are aluminosilicates with the Al in tetrahedral coordination, giving rise to a negative charge that must be compensated for by intracrystalline cations. Another group of IMS are aluminophosphates (AlPOs) with Al and P in tetrahedral coordination forming an electrically neutral network and therefore, without compensation cations and the SAPOs and MAPOs, in which aside from aluminum and phosphorus, there are other elements such as Si and transition metals respectively.
In zeolites, we can adjust the adsorption force by modifying the chemical composition of the network, keeping the structure constant, as it happens when several faujasites with different Si/Al ratios are used; upon modifying this ratio the number of adsorption centers and the force thereof vary. The variation of the Si/Al ratio can be varied by means of synthesis of the zeolite (D. M. Ginger (1992). xe2x80x9cThe chemistry of NaY crystallization from sodium silicate solutionsxe2x80x9d. Molecular Sieves. 1:6-30) or post synthesis, mainly by means of treatment with steam.
Another variable that allows us to adjust the adsorption force, in the case of zeolites, is the modification of the cation charge/radius ratio: Upon exchanging a cation for another one with a smaller charge/radius ratio increases the charge fraction on the oxygen bridge, therefore increasing the interaction of a polar organic semiochemical adsorbed on the zeolite. Cation exchanges tend to be carried out by means of treatment in liquid phase (A. Cremers (1976). xe2x80x9cIon exchange in zeolitesxe2x80x9d. Molecular Sieves. 2:179-193) or in solid phase (H. G. Karge, (1992). xe2x80x9cModification of zeolites and new routes to ion exchangexe2x80x9d. Zeolites Microporous Solids: Synthesis, structure and reactivity. 273-290). In this way, fixation by lipophile for low polarity pheromones can also be varied.
If it is a matter of zeolites, in many cases, we can give them Bronsted acidity in order to cause the formation of hydrogen bonds with the adsorbed semiochemical, when this has functional groups capable of forming said bonds, which causes an increase of retention. The introduction of protons can be done by acid treatment (C. V. McDaniel, P. K. Maher (1976). xe2x80x9cZeolite chemistry and catalysisxe2x80x9d. ACS Monograph. 171:285-299) or exchange with NH4+ and calcination (A. P. Bolton (1976). xe2x80x9cExperimental methods in catalytic researchxe2x80x9d. Academic Press. 2: 1-23) or by direct calcination on samples that do not contain alkaline compensation cations, but rather amines or quaternary ammonium cations.
In IMS we can control the diffusion of molecules through the network by modifying the dimensions of pores and cavities and the size of the compensation cations if there are any. A small pore, but sufficiently large so as to permit the entry of the semiochemical, makes the diffusion thereof difficult and therefore, the semiochemical will have a lower emitting speed. Diffusion can also be controlled by varying the size of the cations: the larger the size the less diffusion and slower emitting speed. The modification of the pore size can be done by modifying the conditions of synthesis of the IMS (A. Corma, Q. Kan, M. T. Navarro, J. Perez-Pariente and F. Rey (1997) xe2x80x9cSynthesis of MCM-41 with different pore diameters without addition of auxiliary organicsxe2x80x9d Chemical Materials. In press).
On the other hand, the fact of compacting the IMS with the adsorbed semiochemical provides us with two more variables, not dependent on the nature of the IMS, in order to control the kinetics:
The compacting pressure: When compacting is done at a higher pressure the amount of semiochemical adsorbed in macropore is reduced and it is forced to diffuse through the network in order to go outside, therefore reducing, the emitting speed.
The surface/weight ratio of the finally obtained form. If the surface/weight ratio is high the semiochemical reaches the surface before, increasing the emitting speed.